This invention relates to airsprings, and in particular, to airsprings having rigid plastic structural components.
The airspring is a pneumatic envelope which can provide load suspension, shock absorption, vibration isolation, actuating or leveling for a wide variety of industrial and automotive applications previously utilizing hydraulic cylinders and steel springs. The airspring utilizes a pair of rigid air retaining structural members with a high strength rubber and fabric, air impervious flex member sealed to the retainers to form the working pneumatic cavity. The form of the flex member may be a straight, relatively tubular form, generally described as a sleeve or a rolling lobe type airspring. In the alternative, the flex member is permanently formed in a convolute configuration, commonly described as a bellows airspring. The retainers in the airspring serve the purpose of structurally connecting two separate portions of the device in which the desired function for the airspring is to be effected. That function may be vibration isolation or actuation between the two portions of the device.
The retainers, thus, are structural members and have conventionally been manufactured from metal. Metal members are commonly cast into a rough configuration, then machined into the exact final form. The machining exposes tiny pores in the cast metal which become air pathways through the metal part and cause air loss from the airspring in service. To overcome this deficiency, high strength plastic and plastic composites which are reinforced have begun to be used in the retainers for airsprings. The plastic rigid components are lightweight, durable and non-porous. These advantages of the plastic structural members such as the retainers have been offset by the problem of providing suitable means for connection of the pneumatic system to the airspring cavity. This connection must be made through one of the rigid airspring retainers. A common method of connecting the pneumatic source to the airspring has been by providing tapered or pipe threading in a bore through the plastic retainer, and subsequently, screwing a threaded connector into the plastic retainer with sufficient torque to seal the connector into the retainer. Several problems are inherent and chronic in this method of attachment including: (1) cross-threading of the coupling into the retainer, thus creating air leaks; (2) over-tightening of the coupling into the plastic retainer causing a split in the rigid airspring retainer member and failure to maintain the structural integrity. When the coupling body is a standard brass NPTF fitting, the brass threads act as cutting edges destroying the originally provided plastic threads.
The problem of air leakage in metal airspring assemblies has been addressed and largely solved by utilizing threaded couplings which screw into the metallic rigid portions of the airsprings. These types of couplings have wholly been unsatisfactory for an airspring with rigid plastic retainers, and a solution to the air leakage problem has eluded the industry. What was recognized was a need to provide an airspring and a method of airspring assembly featuring a coupling which could be easily inserted into the plastic structural member without employing threaded sockets. Also, the fluid conduit or tubing which connects the spring to the pneumatic source should be capable of being pushed into engagement in the coupling and firmly sealed and mechanically held. An object of the invention is to provide an airspring having a built-in coupling which allowed the pneumatic tubing to be pushed vertically into the airspring body while simultaneously providing a reliable air seal and an affirmative mechanical lock of the tubing into the airspring. One feature of the invention is an airspring which has an integral coupling apparatus which is embedded in an orifice in the rigid member of the airspring where the coupling has a ring adapted to be sealingly positioned in the orifice, an annular sleeve with a plurality of jaws adapted for receiving the fluid conduit and affirmatively holding the conduit within the jaws an O-ring seal positioned in the orifice and adapted to seal against the exterior of the fluid conduit. The ring has a flared portion for forcing the jaws of the clamp into full engagement with the exterior surface of the fluid conduit. This type of a coupling configuration avoids the problems associated with the prior method of coupling airsprings having plastic rigid components through which the pneumatic connection was made, and no cross threading, under tightening or over tightening of the coupling is possible, thus avoiding the disadvantages and problems of the prior art. The advantages of this invention may be enjoyed by use of an airspring having at least one plastic rigid member comprising:
an upper retainer;
a lower retainer spaced apart from the upper retainer;
a flexible gas impervious membrane sealably attached to said upper and lower retainers to form a cavity therebetween wherein at least one of said retainers is made of plastic and includes an orifice therethrough in connection with the cavity;
a coupling comprising an annular sleeve including a plurality of jaws adapted for receiving a fluid conduit therein being positioned in said orifice, a ring having a flared portion for forcing the jaws of the annular sleeve radially inward into engagement with the fluid conduit surrounding said sleeve adapted to be sealingly received in said orifice positioned within said orifice and a means for forming a seal between the fluid conduit and the orifice.
In another embodiment of the invention is a method of manufacturing an airspring having a first rigid retainer, a second rigid retainer, a flexible air impervious membrane sealably attached to the retainers to form a working cavity, said method comprising the steps of: (a) sealingly attaching an end of said membrane to each of said first and second retainers to form a working cavity therebetween; (b) forming an orifice through at least one of said first or second retainer, said orifice connecting with said working cavity; (c) inserting an unthreaded coupling assembly into said orifice, said coupling assembly including a ring adapted to be received in the orifice to provide an airtight seal with the retainer, an annular sleeve including a plurality of jaws adapted for receiving a fluid conduit positioned within said ring, an O-ring seal positioned in the orifice inwardly toward said cavity adapted to seal against the fluid conduit, said ring having a flared portion for forcing the plurality of jaws of the sleeve into engagement with the fluid conduit.
The plastic retainer may be formed from any suitable reinforced or non-reinforced thermoplastic or thermosetting synthetic polymeric resin to yield a tough rigid structural member.